Grass for Renewable Energy Production

Reed Canary Grass (RCG) is a well-adapted, long-lived, cool season, perennial native grass that can grow well in wet areas, while also tolerating drier areas. RCG is often harvested in late autumn or early spring, and is primarily used as bedding material. While RCG is a suitable grass for renewable energy production, currently it struggles to compete with other cheaper biomass feedstocks.

One possible way for RCG to compete with cheaper biomass feedstocks is to use it as a bedding material first, and then as a feedstock forbiomass renewable energy production after. By using RCG twice, the theory goes, the costs of cultivation and harvesting the grass for renewable energy production should decrease (making it more competitive).

The test for using RCG for just biogas production involved harvesting the grass around midsummer and again in late August/early September. The test for using RCG for bedding material and biogas production involved harvesting around midsummer and again the following spring, when the grass was dry enough to be used as bedding material.

Two for the Price of One?

Using biomass for two purposes can reduce or increase the cost of bioenergy production. Careful research is therefore required to determine the impact.

Interestingly, the yield of RCG harvested for just biogas production was 7,055kg dry matter/ha, while the yield of RCG for bedding material and biogas production was almost 20% lower at 5,704kg dry matter/ha. This result suggests major dry matter losses occur when RCG remains in the field over the winter and is harvested dry in the spring.

To determine biogas production potential, JTI undertook batch anaerobic digestion tests of the RCG. After 100 days of digestion, the RCG harvested in midsummer had a slightly higher methane yield (327 m3/tonne dry matter) than the grass harvested in late August/early September (305 m3/tonne dry matter). However, this difference was not statistically significant.

Results from the crop trials and the batch digestion tests were then used to calculate costs, revenues and energy consumption for the two tests; just biogas production, and bedding material and biogas production. Calculations show that RCG harvesting costs for just biogas production were much lower ($124/tonne dry matter) than harvesting costs for bedding material and biogas production ($226/tonne dry matter). The main reason for this difference was the need for different harvesting equipment.

Based on the results of this research, an estimated price for RCG for biogas production was calculated as $0.2/kg dry matter from the first harvest in midsummer, and $0.19/kg dry matter from the second harvest in late August/early September. The price of RCG harvested dry in the spring for bedding material was calculated as $0.22/kg dry matter.

For more information about using biomass for renewable energy production, or if you have any questions regarding biomass renewable energy, please contact us.